Poly(butylene succinate) (PBS), also known as poly(tetramethylene succinate), is a thermoplastic polymer formed by polymerization of succinic acid, or of at least one succinic acid diester, such as dimethyl succinate, and of 1,4-butanediol. PBS is well known and used in particular for applications in which its biodegradability is an asset, for example for the manufacture of disposable cutlery, fishing nets, or mulching films. The films are mainly manufactured by film blowing, this technique enabling the manufacture of films of large size, i.e. films which can reach more than a meter in each of its two dimensions. However, in order to manufacture these films by film blowing, it must be possible for the PBS to be stretched in two dimensions in its molten state, this being preferably without any breaking phenomenon being observed during the preparation of the blown film.
PBS is generally obtained in two steps: in a first step, oligomers are manufactured by means of a reaction in which succinic acid or succinic acid diester and 1,4-butanediol are polyesterified. In a second step, the weight of the polymer is increased by carrying out a reaction in which the oligomers obtained during the first step are transesterified. As it happens, during the synthesis of PBS, the polyesterification and transesterification reactions must be sufficiently long if it is desired for the PBS to be capable of being stretched by film blowing. It follows from this that the productivity of the film-blowable PBS is limited by these long reaction times.
The introduction of fumed silica into the PBS can be carried out by melt-mixing of the polymer with the silica as described by Bian et al. (J. Appl Pol. Sci., 2009, 116, 902-912).
This introduction of fumed silica into the composite can also be carried out by reacting the constituent monomers of the polymer with fumed silica, in situ.
The introduction of fumed-silica nanofillers during the preparation of poly(butylene succinate) films and the improvement of the mechanical properties of the product which results therefrom have already been described by Vassiliou et al. (J. Appl. Pol. Sci. 2010, 119, 2010-2024).
Thus, Vassiliou describes an increase in the Young's modulus, the yield stress and the tensile strength, which is accompanied by a decrease in the elongation at break of the poly(butylene succinate) when the amount of fumed silica that is incorporated therein is increased. As it happens, it is important that the materials formed from these composites, in particular blown films, have a high elongation at break and that this elongation is homogeneous, whatever the direction of stress of the material, in particular when these films are used in industrial manufacturing processes.
Furthermore, Vassiliou does not describe the obtaining of a material which is highly film-blowable through the addition of this silica to the PBS.
The preparation of such composites by reaction in situ has also been described by Han et al. (Pol. Deg and Stab., 2008, 116, 889-895).
The applicant has demonstrated that, unexpectedly, the incorporation of colloidal silica during the preparation of PBS makes it possible to obtain a highly film-blowable composite material.
This PBS- and colloidal silica-based composite material can be obtained more rapidly than with the conventional processes for manufacturing film-blowable PBS. It has a high elongation at break, whatever the direction in which the material is stressed.
The applicant has thus also developed a process for the film blowing of films of this composite.